User:Rstrait/2018 California wildfires

Causes
"Several factors led to the destructiveness of the 2018 California wildfire season. A combination of increased fuel loading and atmospheric conditions influenced by global warming led to a series of destructive fires." Primary causes of wildfire vary geographically based on many factors, such as topography. For example, characteristically dense forests in the Sierra Nevada Mountains harbor fuel-driven fires while the open central valley from the south Bay Area to San Diego County are more prone to wind-driven fire over dry grasslands.

Increase in Fuel
"A direct contributor to the 2018 California wildfires was an increase in dead tree fuel. [] By December 2017, there was a record 129 million dead trees in California. []" Tree mortality is linked to a long period during the 2010s of "anomalously warm droughts" that were severe enough to stand out even amongst California's existing history of wildfires and exceptionally dry conditions. Such drought leaves trees stressed for water, which makes them susceptible to beetle infestation and exacerbates tree mortality further. One study focused on the concentrated mortality of densely populated conifers of the Sierra Nevada "found that die-off was closely tied to multi-year deep-rooting-zone drying" and that severity of that dryness can be used to predict mortality.

Drought intensity lessened in California by 2017, but the effects of tree mortality linger for years. One study expresses a lack of sufficient data to confidently determine the rate of coniferous tree decay in the Sierra Nevada. Nonetheless it is a gradual process, and the remaining dead tree matter is an optimal fuel source for future wild fires.

Residential construction in the wildland-urban interface
"A wildland–urban interface (or WUI) refers to the zone of transition between unoccupied land and human development. Communities that are within 0.5 miles (0.80  km) of the zone may also be included. These lands and communities adjacent to and surrounded by wildlands are at risk of wildfires. Since the 1990s, over 43% of new residential buildings have been constructed in this area. In some areas, the amount of new residences in those areas is 80%. In the past, when these areas burned, no residences were lost, but now residences are present, which end up being destroyed. Furthermore, a "century of successful fire suppression" performed in an attempt to protect forests and those living in WUIs has also disrupted natural cycles of disturbance and renewed succession of an ecosystem by allowing fuel to reach abnormal density levels discussed above." Furthermore, a "century of successful fire suppression" performed in an attempt to protect forests and those living in WUIs has also disrupted natural cycles of disturbance and renewed succession of an ecosystem by allowing fuel to reach abnormal density levels discussed above.

Conversely, wet and warm conditions in densely populated forests increase "moisture overdraft" which is when more moisture evaporates from the soil than is returned to the soil by precipitation.

"A forest reconstruction model to assess changes to Sierra Nevada mixed-conifer forest during the fire suppression era" article

(source that says we need more data on coniferous tree decay in the sierra nevada)